I just read about the sperm meets egg plan online and I am a bit confused. It says after the opk comes back positive, to have s_x for three days, skip a day, and then have s_x again. The opk I use (the cheapest at walmart), says the surge happens 24-36 hours after I get a positive. If the egg only lasts for 12-24 hours, is the SMEP missing the window at the end?

No, b/c up to that point you're having it every other day- so, you are covered. B/c opk's are pos for 24-36 hrs, you are catching it. The extra day is just in case. It's the plan I used (tried to, but never really saw pos.opk- although Fertilityfriend says we got the 3 days before, skipped the O day, and got the day after. We'll see if it worked. Under the Stacey strand is where we were talking about it.